We permanently live in France, and are tax and fiscally resident here, consequently we don't have a UK address but we do have a widebeam in the UK for our own holiday use.
When making recent enquiries with the TV licensing people I was advised that I would need a license, however as we do not have a UK address etc etc, the solution they proposed would be for me to have a monthly direct debit for the license, but cancel it when we're not on the boat. Thereby only actually having it for the times when we're there.
Just in case this is of any use to any other expat boaters..